Field of the Invention
This invention relates to turbochargers, and in particular provides a bearing housing with the oil, water and air galleries formed by casting the bearing housing casting material around pre-staged pipes.
Description of the Related Art
Turbochargers extract energy from a vehicle exhaust to drive a compressor to deliver air at high density to the engine intake, allowing more fuel to be combusted, thus boosting the engine's horsepower. The rotating assembly of the turbocharger, comprising turbine wheel, compressor wheel, and shaft, may rotate at 80,000 RPM to 300,000 RPM. The shaft rotates on a hydrodynamic bearing system. Oil is fed, under pressure, to an oil fitting in top of the bearing housing, from which it travels in oil bores to the journal bearings (33, 34) and the thrust bearing (35).
Conventionally, a bearing housing is cast without oil bores. The bores are subsequently machined into the bearing housing by drilling along a straight line. Typically a drill guide is used to support a drill or boring tool, and drilling access for this drill guide (94, 95) can only be through the axially open ends of the relatively small-diameter journal bearing bore (65) of the bearing housing. This is a very awkward machining feat often requiring intricate tooling as the drill must first start, at a very shallow angle, at the correct place in the journal bearing bore, and then break through the as-cast oil delivery bore. Due to limited access for the drilling tool, the resulting bore for delivering oil to the journal bearing is at an angle to the journal bearing bore and located close to the end of the bearing housing.
The thrust bearing oil feed bore (69) is also a straight line bore that typically must intersect not only the two journal bearing oil feed bores (67, 68), but also the feed bore (62) from the oil inlet. The resultant of these geometry of these bores is typically that the breakout of the thrust bearing oil feed bore (69) in the thrust bearing mounting face (85) is at a larger offset from the centerline than is desirable, in particular because this results in the canal of the thrust bearing being at a larger radius from the turbocharger centerline than desired, as a result of which the thrust bearing must be larger than desired, which elevates the material cost.
Most turbochargers mount to the engine via the turbine housing foot. In some cases, instead of oil being fed via a pressurized tube or pipe to a fitting on top of the bearing housing, the turbochargers are mounted to an engine mount via a foot which extends from the bottom of the bearing housing and includes a connection through which pressurized engine oil is fed to the bearing housing and a connection for draining the bearing housing to a cavity within the engine component. Connections may also be provided for water-cooling the bearing housing.
A problem with such configurations is that the oil feed must travel vertically up from the bearing housing foot (70), across to a point above each journal bearing, and then vertically down into the journal bearings. With the current state of the art, several drillings are required to describe the oil flow path. This also means that some oil bore drillings have to be drilled from outside the bearing housing to intersect other bores; and then the unused part of the bore must be sealed off with plugs to complete the oil flow circuit. Such a manufacturing method also means that corners in the flow path are sharp with no radius to very little radius, which is not conducive to good fluid flow with low losses.
Further, potentially damaging metal burrs are produced by this metal-removing manufacturing method, and also as a result from the break-through of the bores into one another. Once machined, the areas in which the minor machined oil delivery bores breakout into the major gallery must be completely deburred to prevent metal burrs from entering the oil flow into tightly toleranced bearing clearances. Failure to deburr these areas well could result in a metal burr entering the bearing and destroying it. These bores are thus time consuming to fabricate, and there always exists the potential for a plug to fall out and thus release engine oil, at pressure, into the very hot environment around the engine and turbocharger.
So it can be seen that there exists the need for a better way of providing oil feed bores in a turbocharger to minimize the complex and difficult machining operations.